Motor control system



MOTOR CONTROL SYSTEM Filed May 16, 1928 Inventor:

Ha' ry AL \A/inne b zZw/amw His Attorney Patented June 30,1931

UNITED STATES PATENT OFFICE HARRY A. Wm, 01 SOHEN'EOTADY, NEW YORK,ASSIGNOR '20 GENERAL ELECTRIC COMPANY, A. CORPORATION OF YOIQK MOTORcommon sirsrmr Application filed Kay 16,

My invention relates to electric motor control systems, moreparticularly to control systems" for electric motors employed to drivereels for winding up strip materials,

5 such as cold rolled strip steel, and has for its object the provisionof a control system for the driving motor which is of simpleconstruction and which is convenient and efiicient in operation. 7

In the manufacture of various sheet materials such as cold rolled stripsteel, the finished product is wound on reels. In winding the materialon the reel it is desirable not only to main a constant tension in thematerial while it is being wound, but also to maintain a tension in thematerial when the mill is stopped so that the material will remaintightly wound upon the reel. My invention, therefore, contemplates thepromsion of control'means for the reel driving motor whereby regardlessof the speed of mill operation, a predetermined constant pull will beexterted upon the material being wound, and whereby when the mill isstopped the material will be held under a desired tension.

In carrying my invention into effect in one form thereof, I rovide thereel driving motor with a contro system which includes a current relator jointly dependent upon a function of the feed of the material tothe reel and the armature current of the motor so that the motor willoperate to maintain a constant tension in the material as it is be ingwound. The control system further includes means responsive to the speedof the strip for causing a certain amount of resistance to be insertedin the motor power circuit when the speed of the strip has been reducedto a .predetermined value so that the motor will maintain the stripunder tension even though the mill is brought to rest.

For a more complete understanding of my invention reference should behad to the accompanying drawing in which the single figure is adiagrammatic representation of a system of control embodying myinvention.

Referring to the drawing, I have shown my invention in one form asapplied to a 1928. Serial No. 278,248.

direct current motor em loyed to drive the collecting reel of a colrolled strip steel r'nill. As shown, a direct current motor 10, providedwith an armature 11 and a field winding 12, is directly connected todrive a reel 13 which serves to collect and wind the strip material 14passing from the last stand of the main finishing rolls 15. A suitablesource of direct current supply '16, preferably of substantiallyconstant voltage, is provided for the motor 10, both the armature 11 andthe field winding 12 being supplied by the source 16. A switch 17 isinserted in the connections "between the armature 11 and the source 16.Any suitable means may.

be provided for'driving the finishing rolls 15. As shown, an electricmotor 18 is provided for this purpose, the motor 18 preferably being ofthe adjustable speed direct current type and supplied with power fromthe source 16. A switch 18a is inserted in the connections between themotor 18 and the source 16.

It will be understood that in the manufacture of cold rolled strip steeland similar materials it is desirable to maintain a certain constanttension in the material between the last stand finishing rolls and thewinding reel. It will be further understood that as long as the linealspeed of the strip the reel motor must be constant in order to maintaina constant tension in the strip. Therefore, in order to maintain aconstant tension inthe strip under all conditions, the horse power inputto the reel motor must increase or decrease proportionately as the speedof the last stand rolls increases or degiven constant speed of the motor18, the

eld of the motor 10 must be gradually in- 30 remains, constant, thehorse power input to creased with the gradual increase in the effectivediameter of the reel 13 in order to maintain a constant current input tothe motor.

In order that the current input to the motor 10 may be so regulated thata predetermined constant tension will be maintained in the strip 14,suitable control means are provided for the motor. The control meanscomprises a regulator 19, which is provided not only for regulating thecurrent input to the motor, so as to maintain the current substantiallyconstant, by varying the speed of the motor 10 according to variationsin the effective diameter of the reel 13, but also for adjusting thecurrent input to compensate for variations in the lineal speed of thestrip.

As shown, the regulator 19 comprises a bar 20 pivoted at a pointadjacent its center, a coil 21 having its core connected to the bar 20at one end thereof, and a coil 22 having its core connected to the bar20 at a point adjacent its other end. The coil 21 is connected across ashunt in the circuit of the armature 11 of the reel motor so that thecurrent in the coil and consequently its pull on its core areproportional to the current drawn by the motor 10 from the source 16.The pull exerted by the coil 22 should be proportional to the speed ofthe last stand rolls, and in order to effect this proportionality asuitable pilot generator 25, provided with an armature 26, and a fieldwinding 27 excited from the source 16, is mounted to be driven by themain driving motor 18. The coil 22 is connected across the armature 26of the generator so that its pull upon its core will be proportional tothe voltage of the generator and consequently to the speed of the laststand rolls.

The regulator 19 is provided with contacts 30 connected across anadjustable resistance 31 which is in turn connected in the circuit ofthe reel motor field winding 12 so that when the contacts are open theresistance will be inserted in the field circuit and when the contactsare closed the resistance will be short circuited. It will be understoodthat normally the control switch 33 will be thrown toward the left, asviewed in the figure, so that the short circuit may be completed for theresistance 31. It will be observed therefore, that the strength of thefield 12 and consequently the current intake of the motor 10 will dependupon the relative values of the currents that energize the coils 21 and22. The regulator is so adjusted that when the current in the reel motorarmature is less than a predetermined value to be maintained to give thedesired tension in the strip, the pull of the coil 21 will beoverbalanced by that of the coil 22 and the contacts 30 will be held intheir open position, thus inserting the resistance 31 in the circuit ofthe field 12. The field will then be weakened which will cause morecurrent to flow through the armature 11. It will be understood thatsince the reel motor speed is fixed by the speed at which the strip isfed to the reel, the speed of the reel motor will remain constantnotwithstanding its field variations as long as the strip speed remainsconstant. When the current in the armature 11 increases to a value abovethe predetermined current to be maintained, the pull exerted by the coil21 will increase to such a degree that the coil 22 will be overpoweredand the contacts 30 will be closed to short circuit the resistance 31whereby the strength of the field 12 will be increased. As a result, themotor 10 will draw less current from the line until when the armaturecurrent is less than the predetermined value the coil 21 will beoverpowered by the coil 22 and the contacts 30 will be opened tore-insert the resistance in the field circuit. The motor current willnow increase and the cycle of operation will be repeated as pre viouslydescribed. The regulator 19 will thus have a vibratory motion,alternately short circuiting and inserting the resistance 31 in thefield circuit of the motor 10. As the contacts rapidly vibrate, theeffective resistance in the field circuit will depend upon theproportion of time that the contacts are in their open position, andassuming that the motor 18 runs at a constant speed, the Vibrator 19will maintain a constant current input to the motor 10 whereby the motorwill apply a constant tension to the strip 14. An anti-hunting coil 32is provided for assisting the coils 21 and 22 to efiect the vibratorymotion. This coil 32 has its core connected to the bar 20 so that thecoil will act in opposition to the coil 21, and as :iIUV, 11 its core isconnected to the same end of the bar as the core of the coil 21. Asshown. the coil 32 is connected in series in the cir cuit of the field12 so that as soon as the contacts 30 are closed the momentary increasein the field current will cause the pull exerted by the coil 32 upon itscore to increase, whereby the coil 22 with the assistance of the coil 32will immediately open the contacts 30.

' Even though the motor 18 runs at a constant speed, the speed of thereel motor 10 must gradually decrease since the effective diameter ofthe reel 13 gradually increases, due to the winding of the strip 14. Asthe reel diameter increases the reel speed obviously decreases and as aresult the motor will tend to apply a torque of such increased valuethat unless suitably compensated for there would result an increase inthe tension in the strip. This action of the motor however causes itsarmature current to increase whereby the regulator operates to close thecontacts 30 and strengthen the mtor field until the armature current hasbeen that the contacts 30 rema n closed will gradually increase. As aresult of this action in maintaining the armature current constant, theeffective field resistance will be gradually reduced and the motor fieldcurrent thereby increased with the result that the motor torque isincreased so as to maintain a constant tension in the strip 14.

It is often desired to adjust the tension in the strip 14 to differentvalues. To eifect this adjustment, an adjustable rheostat 34 isconnected in series with the coil 22 of the regulator 19. Assuming thatthe generator 25 is running at a constant speed and it is desired todecrease-the tension in the strip, the resistance 34 will be increasedso that the current in the coil 22 will be decreased. Consequently, thepull exerted by the coil 22 upon the bar 20 will decrease and theresistance 31 will be short circuited for a greater portion of time,whereby the field 12 will be strengthened and the armature current ofthe motor will be decreased to a value sufiicient to correspond to thereduced pull of the coil 22, and will be held at its decreased value bythe vibratory action of the regulator 19. It will be understood that thetension upon the strip will be decreased proportionately with thedecrease in the armature current. Similiarly by decreasing theresistance 34 the tension upon the strip will be increased.

Any variation in speed of the rolls re sults in a change in the voltageapplied to the coil 22 by the generator and consequently in a change inthe current setting of the regulator whereby a different current will bemaintained in the armature of the motor 10 so as to maintain thepredetermined tension in the strip. Assuming that the speed of the laststand rolls increases, the voltage of the pilot generator 25 willincrease and consequently the pull of coil 22 will increaseproportionately to the increase in speed. To balance the increased pullof the coil 22, the pull of the coil 21 must increase which means thatthe current and consequently the horse power input to the-motor 10 mustincrease correspondingly. This will be accomplished by the regulator 19which will hold the contacts open for a greater proportion of the time,thereby increasing the effective resistance in the field circuit of thereel motor so that its speed will increase proportionately with theincrease in the speed of the main motor 18. Should the speed of the laststand rolls be decreased, the pull exerted by the coil 22 will bedecreased and the current and consequently the horse power input to themotor 10 will be proportionatelydecreased so that its speed will bereduced in accordance with the reduction in speed of the main motor.

In order that the work upon the regulator 19 may be materially reduced,a suitable adjustable rheostat 35 is inserted in the circuit of thefield 12. This rheostat may be adjusted to take care of changes in speedof the reel motor due to changes in speed of the motor 18. If desired,this resistance may be mechanically connected to the rheostat connectedin the field of the motor 18, so that as the operator varies theresistance in the field of the motor 18, the resistance in the field ofthe motor 10 will be automatically and proportionately varied. Thus withthis arrangement, the rheostat 35 will automatically tend to adjust thespeed of the reel motor as the speed of the main roll is adjusted. It isto be understood, however, that the rheostat 35 is provided merely toreduce the work upon the regulator, and that the regulator may whollyperform the function of accurately varying the current input to themotor 10 according to variations .in the speed. of the strip 14, as wellas maintaining constant tension with a fixed speed of the strip.

It will be understood that the motor 10 is provided with startingresistance connected in series with its armature. As shown, the startingresistance 40 is connected in series with the motor armature 11,accelerating contactors 41, 42 and 43 being provided to progressivelyshort circuit this resistance when the motor is started up. Thesecontactors are controlled by suitable accelerating relays 44 in any wellknown manner.

The starting resistance 40 is also advantageously employed to allow acertain pull to be applied to the strip even though the mill is shutdown. The return circuits of the contactors 41 and 42 are controlled bya relay 45. The relay 45 is connected across the armature 26 of thepilot generator and is so adjusted that it will open its contactswhenever the voltage of the generator drops below a preedtermined value.Thus if the generator voltage drops below the predetermined value, thecontacts of the relay 45 will open and the accelerating contactors 41and 42 will open and a certain amount of the starting resistance 40 willbe inserted in series with the motor armature 11. Consequently, if .theoperator should shut the mill down, as the speed of the strip drops to acertain predetermined value, the relay 45 will open its contact andinsert the resistance in series with the reel motor armature so that thecurrent to the armature will be limited by this resistance.Consequently, as the mill comes to rest, the reel motor may be leftconnected to its supply circuit and a certain amount oftension will bemaintained in the strip due to the current which will still be flowingthrough the armature of the reel motor. \Vhcn the main roll motor 18 isagain started up and the volta e of the generator 25 builds up to apredetermined value, the relay 45 will pick up and close its contactswhereby the contactors 41 and 42 will be closed in succession and fullvoltage applied to the reel motor armature.

In operation, it will be understood that the main motor 18 drives themain rolls 15 at any desired speed and that the motor 10 operates tomaintain a certain predetermined tension in the strip 14 as determinedby the adjustment of the rheostat 34:. When the motor 18 operates at aconstant speed, the regulator 19 will operate to maintain a constantcurrent input to the motor 10 so that it will maintain this desiredconstant tension in the strip. The regulator 19 further controls thecurrent input to the motor 10 by gradually decreasing its speed as theefiective diameter of the reel gradually increases lVhen the motor 18 isadjusted to run at higher or lower speeds, the regulator 19, assisted byappropriate adjustment of the rheostat 35, will automatically adjust theeffective resistance in the field circuit of the motor 10 so that itwill operate at lower or higher speeds accordingly, whereby regardlessof the speed of the mill any desired predetermined tension will beconstantly maintained in the strip 14.

lVhen threading a strip in the reel to start a new coil the motor 10must be run at a slow speed to permit the threading operation. To effectthis, a push button 50 is so connected in the field winding circuit ofthe motor 10 that when it is closed the resistances 31 and 35 will beshort circuited where by full field strength will be applied to the reelmotor, as a result of which it will run at a very slow speed as long asbutton 50 is held in its closed position. On the other hand it may bedesired to operate the reel motor at full speed when the mill itself isnot running at all. In order to so operate the motor 10 the switch 33 ismoved to its right hand position, as viewed in the figure, whereby theregulator is cut out and the contacts of the relay 45, which have beenopened as the mill slowed down, are shortcircuited so that theaccelerating contactors 40 and -11 will be allowed to close and allresistance thus cut out of the motor armature circuit. The motor willthen operate at its full speed.

\Vhile I have described a particular em bodiment of my inventionoperating in a particular manner in accordance with the provisions ofthe patent statutes, it should be understood that I do not limit myinvention thereto since various modifications thereof will suggestthemselves to those skilled in the art without departing from the spiritof my invention the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The combination with a winding reel for a strip of material to bewound thereon, of means for feeding said strip to said reel, an electricdriving motor for said reel, a source of electrical supply for said reeldriving motor having a substantially constant potential irrespective ofthe feed of said strip to said reel and means dependent upon a functionof the feed of said strip to said reel and the driving motor current forregulating said driving motor so as to maintain a tension in said strip.

2. The combination with a winding reel for a strip of material to bewound thereon, of means for feeding said strip to said reel, an electricdriving motor for said reel, a source of electrical supply for saidmotor having a substantiall constant potential irrespective of the feeof said strip to said reel, and means jointly responsive to the rate offeed of said strip and to the driving motor current for regulating saiddrivi 0 motor so as to vary the current input thereto proportionatelywith the rate of feed of said strip.

3. The combination with a winding reel for a strip of material to bewound thereon, of an electric driving motor for said reel and aregulator jointly responsive to the rate of feed of said strip and tothe driving motor current for regulating said driving motor so as tovary the current input thereto proportionately with the rate of feed ofsaid strip.

4. The combination with a winding reel for a strip of material to bewound thereon, of a driving motor forsaid reel, a resistance adapted tobe inserted in the circuit of the field winding of said motor, andvibratory controlling means for said resistance whereby said resistanceis periodically inserted in the field circuit of said motor, saidvibratory controlling means being responsive to the armature current ofsaid motor and to the speed of said strip, whereby the current input tosaid motor is varied proportionately with the speed of said strip.

5. The combination with a winding reel for a strip of material to bewound thereon, of an operating motor for said winding reel, asubstantially constant voltage source of electrical supply for saidoperating motor, an electric generator driven at a speed proportional tothe speed of said strip, and a regulator electrically responsive to thevoltage of said generator and to the armature current of said operatingmotor for governing the current input to said operating motor whereby atension is maintained in said strip.

6. The combination with a winding reel for a strip of material to bewound thereon, of an operating motor for said winding reel, a resistanceadapted to be inserted in the field circuit of said operating motor, anelectric generator driven at a speed proportional to the lineal speed ofsaid strip, and means electrically responsive to the voltage of saidgenerator and to the armature current of said operating motor forregulating the insertion of said resistance whereby the current input tosaid operating motor is varied directly with the lineal speed of saidstrip.

7. The combination with a winding reel for a strip of material to bewound thereon, of an operating motor for said winding reel, a resistanceadapted to be inserted in the field circuit of said operating motor,adjusting means for said resistance responsive to the speed of saidstrip and the armature current of said operating motor whereby thestrength of said field winding is varied to cause the current input tosaid operating motor to vary directly with the speed of said strip, andcircuit controlling means independent of said resistance adjusting meansinserted in the field winding circuit whereby said resistance may beby-passed so as to permit said operating motor to run at its minimumspeed.

8. The combination with a winding reel for a strip of material to bewound thereon, operating means for delivering said strip to said windingreel, a driving motor for said winding reel and a regulator for saiddriving motor jointly responsive to a function of the delivery speed andto the driving motor current for varying the horse power input to saiddriving motor so as to maintain a tension in said strip.

9. The combination with a winding ree for a strip of material to bewound thereon, operating means for delivering said strip to said windingreel, a driving motor for said winding reel, a resistance ada ted to beinserted in the circuit of the fie d winding of said driving motor, agenerator driven at a speed proportionate to the delivery of said strip,and means for regulating the insertion of said resistance whereby thestrength of the field of said driving motor is varied to vary thecurrent input to the driving motor directly with the speed of said stripsaid regulating means comprising a pair of electrical contacts shuntedacross said resist ance, said contacts when opened inserting saidresistance in the field circuit and when closed by-passing saidresistance, an electromagnet responsive to the voltage of said generatorfor opening said contacts, and an electromagnet opposed to said firstelectromagnet and responsive to the armature cur rent of said drivingmotor for closing said contacts.

10. The combination with a winding reel for a strip of material to bewound thereon, operating means for delivering said strip to said reel,an electric motor for driving said winding reel, a source of electricalenergy for said driving motor having a substantially constant potentialirrespective of the rate of delivery of said strip to said reel, a

resistance adapted to be inserted in the circuit between said source andsaid driving motor, controlling means for said resistance responsive tothe speed of said strip to said reel whereby when the speed of saidstrip has been reduced to a predetermined value said resistance will beinserted in the driving motor circuit so that said driving motor will.maintain a tension in said strip whenthe strip has beenstopped.

11. The combination with a winding reel for a strip of material to bewound thereon, operating means for delivering said strip to said windingreel, an electric motor for driving said reel, starting resistance forsaid driving motor, an electric generator driven at a speed proportionalto the speed of said strip to said reel, regulating means for saiddriving motor jointly responsive to the armature current of said drivingmotor and to the voltage of said generator for varying the horse powerinput to said driving motor directly with the speed of said strip, and arelay for controlling said resistance responsive to the voltage of saidgenerator, whereby when the speed of said strip has dropped to apredetermined value a portion of said starting resistance will beinserted in the motor circuit so as to cause said driving motor tothereafter maintain a tension of predetermined value in said strip.

In witness whereof I have hereunto set my hand this 15th day of May,1928.

HARRY A. WINNE.

